The present invention relates to a press frame, and more particularly to a frame of a mechanical press which is provided with adjustment means between the crown part of the press which supports the rotating shaft of the press carrying the upper die and the bed part, and which operate in the direction to increase or reduce the distance between the two parts.
Among the types of frames for mechanical presses, there are a frame which is composed of separate parts, i.e., a crown, columns, and a bed, which parts are secured together by tie rods, and a unitary type frame in which all these parts are unified in a single body. In either type frame, the length of the rods connecting the crank shaft and the slide may be increased due to heat from the bearings for the rotation member which is generated when the press is operated, and consequently the distance between the upper die mounted on the slide and the lower die fixed to the bolster is liable to vary between the time of the start of the operation of the press to the time when normal operation is under way.
Reference is made to FIG. 7, which shows a frame of a mechanical press in accordance with the prior art and which is made up of separate parts. Connecting means extend between a crown 1 and a body 2 and are constituted by hollow columns 3 supporting the crown 1 on the bed 2, and tie rods 4 extending through the columns 3. These tie rods 4 extend through and protrude from the crown 1 and the bed 2, and the protruding upper and lower ends are secured by nuts 5, thus holding the press frame in the assembled condition. A slide 6 housed within the columns 3 is connected to rods 7 which are operated by a rotating shaft or crank shaft in the crown 1. An upper die 8 is mounted on the slide 6, and a lower die 9 is mounted on the bed 2.
Because the cross-sectional areas of the connecting rods 7 are small relative to their lengths, heat will cause an increase in length in the longitudinal direction, thereby changing the position of the slide, and reducing the distance between the upper and the lower dies. Such heat can come from the bearings supporting the crank shaft in the crown 1 which is generated during operation of the press.
In a blanking operation, changes in distance between the upper and the lower dies cause the blanking punch to go farther into the die more than desired, and thus damage the dies. In a coining operation, the upper die descends past a predetermined lower position, and thus products come out thinner. In both instances, overload is caused in the drive part of the press frame, reducing the working life of the press.
Also, when two work pieces are accidentally supplied simultaneously during press operation, a very large overload is exerted on the dies, creating a so-called "sticking" condition, a condition in which the power supplied to the crank shaft is insufficient to drive it past the bottom dead center position. In order to restore the operation of the press after occurrence of such a condition, it has been necessary to provide a special device.
In the prior art there has been, as far as is known, only one means for protecting presses from the drawback referred to above, namely means for adjustment of the slide, or a so-called die gap adjustment means.